1. Field of the Invention
This invention relates to a method and device for controlling energization of a high pressure electromagnetic valve, and more particularly to improvements in a method and a device for controlling energization of a high pressure electromagnetic valve, suitable for use in an electronically controlled diesel engine for a motor vehicle, wherein a time period of energization is controlled in accordance with a target value of a fuel injection quantity obtained from at least an engine speed and an engine load.
2. Description of the Background Art
Along with the development in electronic control techniques, particularly, digital control techniques in recent years, a so-called electronically controlled diesel engine, wherein a fuel injection pump is electronically controlled, has been commercialized.
There are various methods of electronically controlling the fuel injection pump, and one of these methods is the method of using a so-called electromagnetic spill type fuel injection pump, wherein spill of fuel in the fuel injection pump is controlled by an electromagnetic valve. In this electromagnetic spill type fuel injection pump, when the fuel injection quantity reaches a target value, a spill port is released to control the end of fuel feed under pressure by a high pressure electromagnetic valve, thus controlling the fuel injection quantity.
A flow control device using a spool valve is disclosed in U.S. Pat. No. 4,480,619.
Control of the energization of an electromagnetic spill valve has heretofore been effected at all times, without considering a target indicated value of a fuel injection quantity determined from at least an engine speed and an engine load. This has been true even when a target value of the fuel injection quantity is 0 mm.sup.3 /st (cubic milimeters/stroke) and a target indicated value of the fuel injection quantity is zero. Therefore, the electromagnetic spill valve is continuously energized and the duty cycle of the electromagnetic spill valve is increased. Thus, the reliability of the valve is decreased. Furthermore, when the electromagnetic spill valve is actuated, a coil section generates heat thus reducing the reliability of the valve. Further, when control of energization is active, even if the time period of energization is shortened, a small quantity of fuel is injected. This results in the disadvantagous generation of white exhaust smoke and the deterioration of fuel consumption performance. More specifically, if the electromagnetic spill valve is turned on and then off, the electromagnetic spill valve is delayed in response, and the time period during which the valve is closed, is prolonged, whereby inner pressure in the valve plunger is instantaneously raised and the fuel leaks.